In analogy to spontaneous breaking of continuous space translation symmetry in the process of space crystal formation, it was proposed that spontaneous breaking of continuous time translation symmetry could lead to time crystal formation. In other words, a time-independent system prepared in the energy ground state is expected to reveal periodic motion under infinitely weak perturbation. In the case of the system proposed originally by Frank Wilczek, spontaneous breaking of time translation symmetry can not be observed if one starts with the ground state. We point out that the symmetry breaking can take place if the system is prepared in an excited eigenstate. The latter can be realized experimentally in ultra-cold atomic gases. We simulate the process of the spontaneous symmetry breaking due to measurements of particle positions and analyze the lifetime of the resulting symmetry broken state. 03.75.Lm, Hamiltonians of condensed matter systems are invariant under translation of all particles by the same vector in space and so are the eigenstates. Consequently probability density for detection of a single particle must be uniform in space if a system is prepared in the ground state or any other eigenstate. Space crystals emerge due to spontaneous symmetry breaking that can be induced by an external perturbation or by, e.g., measurements of particle positions. If the single particle probability density is uniform but the density-density correlation function reveals periodic behavior, measurement of a position of a particle breaks the continuous space translation symmetry and the probability density for the detection of a next particle shows crystalline structure [1, 2]. In the thermodynamic limit, the lifetime of the symmetry broken state goes to infinity and the stable space crystal is formed.Similar phenomenon was postulated to exist in the time domain [3]. A spontaneous breaking of the continuous time translation symmetry in the ground state of the model system was suggested to lead to a periodic motion of a nonuniform density. Soon the other experiment involving trapped ions in a ring [4] was proposed. However, at the same time the original proposition has been put in question [5,6]. While the discussion interestingly evolved [7][8][9][10][11][12][13] strong arguments have been presented [14][15][16] against the existence of time crystals. The proposals, nevertheless, became inspiring and triggered a new field of research. It turns out that, by analogy to condensed matter physics, where space periodic potentials allow for modeling of space crystals, periodically driven systems can model crystalline behavior in time [17]. Anderson localization and Mott insulator phase in the time domain can be realized [18][19][20] and spontaneous breaking of discrete time translation symmetry to another discrete symmetry can be investigated [17]. The latter phenomenon, termed discrete time crystal, was recently observed in two experiments [21,22] following independent theoretical suggestions [23][24][25][26][27][28][29]. Thos...